The typical operations of a large-scale chemical processing facility such as a refinery may generate significant amount of hazardous air pollutants (HAP) as a component of the off-gas released from storage vessels, process vents, and wastewater equipment associated with refinery operations. Governmental regulations typically require the removal of a significant portion of these off-gas HAPs. For example, the USEPA National Emission Standards for Hazardous Air Pollutants (NESHAP) requires the removal of 95% or more of HAPs prior to releasing the off-gases into the environment. Regulations are even more stringent for volatile organic compounds such as benzene or VOC; the Benzene or VOC Waste Operations NESHAP regulations require 98% removal of off-gas benzene or VOC using one or more approved control technologies.
Commonly used control technologies include vapor phase adsorption, in which the benzene and other VOCs are selectively collected out of the out-gas on the surface of a porous solid such as activated carbon. Another common control technology used to eliminate VOCs from the off-gases is incineration by thermal incinerators, such as flares, or catalytic incinerators, such as fluid-bed catalytic incinerators, in which a combustion reaction is used to convert the VOCs into CO2 and water. Most of the commonly used control technologies are typically expensive to operate and generate high carbon footprints. Alternative Control Devices including bioreactors, such as activated sludge biotreatment devices, have more recently just begun to gain regulatory acceptance and use in industry.
Activated sludge biotreatment devices eliminate the VOCs in off-gases by venting the off-gases through a tank containing the activated sludge which includes various microbes such as bacteria and protozoa. The activated sludge in the tank of the biotreatment devices may digest the VOCs, convert the VOCs into additional biomass, biodegrade the VOCs into CO2 and water, or any combination of these treatments. The activated sludge may be recycled indefinitely, and the activated sludge biotreatment devices may be operated at minimal cost and energy consumption. Once established, activated sludge biotreatment devices may prove to be highly efficient and sustainable Alternative Control Devices.
When implementing the use of any Alternative Control Device in an industrial setting, full-scale verification of the performance of the control technology may be conducted to ensure that the control technology possesses sufficient capacity and robustness to function effectively under the full range of operating conditions experienced in the industrial environment, and to demonstrate regulatory compliance. In the case of bioreactor devices such as activated sludge biotreatment devices, a flux chamber is a common method of evaluating VOC emissions from a full-scale, operating bioreactor. A Flux Chamber monitors off-gas emissions directly from the surface of the bioreactor using VOC measurements obtained by one or more small floating plastic spheres at selected sampling points on the surface of the bioreactor tank. However, one disadvantage of the Flux Chamber method is that there exists no expedient control of the operating parameters of the bioreactor during performance testing, and due to the exposure of the small plastic spheres to the external environment, the Flux Chamber measurements may be highly susceptible to external conditions, such as a stray oil drop. As a result, there may be limited ability of the full-scale operating biosystem to modify operations in order to correct an abnormal occurrence, or to adjust operating conditions in order to identify the maximum stress conditions at which the biosystem may operate effectively.
A need exists in the art for a device which may be used for the assessment of the efficacy of a bioreactor device that possesses expedient control of the operating parameters of the bioreactor device and is not susceptible to external conditions. Such a device may be used to assess the efficacy of the bioreactor device as an Alternative Control Device for the removal of VOCs such as benzene or other VOCs from industrial off-gases in order to demonstrate regulatory compliance or to explore the range of conditions under which the bioreactor may operate effectively. Further, such a device may be used to establish initial operating conditions for the bioreactor device based on the on-site environmental conditions, or the device may be used to explore the effects of variation of the operating conditions on the efficacy of the bioreactor device in order to enhance the efficacy of the device.